Interest in the percutaneous or transdermal sampling of agents continues to grow. The transdermal sampling of agents still faces significant problems. In many instances, the flux of agents through the skin is insufficient to calculate quickly and accurately the concentration of the sampled substance in the blood or body.
One method of increasing the transdermal sampling of agents relies on the application of an electric current across the body surface or on "electrotransport". "Electrotransport" refers generally to the passage of an agent through a body surface such as skin, mucous membranes, nails, and the like. The transport of the agent is induced or enhanced by the application of an electrical potential, which results in the application of electric current, which samples or enhances sampling of the agent. The electrotransport of agents through a body surface may be attained in various manners. One widely used electrotransport process, iontophoresis, involves the electrically induced transport of charged ions. Electroosmosis, another type of electrotransport process, involves the movement of a solvent with the agent through a membrane under the influence of an electric field. Electroporation, still another type of electrotransport, involves the passage of an agent through pores formed by applying a high voltage electrical pulse to a membrane. In many instances, more than one of these processes may be occurring simultaneously to different extents. Further increases in transdermal sampling rates are highly desirable.
One method of increasing the agent transdermal sampling rate involves pre-treating the skin with a skin permeation enhancer. The term "permeation enhancer" is broadly used herein to describe a substance which, when applied to a body surface through which the agent is sampled, enhances its transdermal flux. The mechanism may involve an increase in the permeability of the body surface, or in the case of electrotransport sampling, a reduction of the electrical resistance of the body surface to the passage of the agent therethrough and/or the creation of hydrophilic pathways through the body surface during electrotransport.
There have been many attempts to enhance transdermal flux by mechanically puncturing the skin prior to transdermal drug delivery. See for example U.S. Pat. No. 5,279,544 issued to Gross et al., U.S. Pat. No. 5,250,023 issued to Lee et al., and U.S. Pat. No. 3,964,482 issued to Gerstel et al. These devices utilize tubular or cylindrical structures generally, although Gerstel does disclose the use of other shapes, to pierce the outer layer of the skin for agent delivery, but not sampling. Each of these devices provide manufacturing challenges, limited mechanical attachment of the structure to the skin, and/or undesirable irritation of the skin.
As has been discussed, a variety of chemicals and mechanical means have been explored to enhance transdermal flux. However, there is still a need to provide a device suitable for increasing transdermal flux which device is low-cost and which can be manufactured reproducibly (i.e., without significant variation from device to device) in high volume production.